The structure-function relationships and mechanisms of phosphoryl transferring enzymes as exemplified by porcine muscle adenylate and yeast 3-phospho-glycerate kinases and nucleotidyl transferring enzymes as exemplified by aminoacyl tRNA synthetases will be investigated by magnetic resonance techniques. Proton NMR and paramagnetic probes will be used to identify substrates and inhibitors. P31-NMR will be used to characterize (1) the environment of each phosphate (2) the interaction of metal ions (3) the equilibrium constants at stoichiometric amounts of enzyme, and (4) the rates of interconversion of bound substrates and products, E. S1S2 yields (reversibly) E.P1P2 for 3-phospho-glycerate kinase and for the first step of methionyl tRNA synthetase reaction. To study the specificity of the second step of the latter enzyme, the structure of F19-uracil substituted tRNA val, in the presence and absence of its cognate enzyme will be investigated by F19-NMR. Hopefully, a pattern will emerge from these experiments concerning the specificity of binding and the conformational changes related to catalysis. Lastly, to verify the occurrence of an aminoacyl-enzyme intermediate between the aminoacyl adenylate and aminoacyl tRna will be investigated by following the appearance of O18 in the alpha-beta bridge oxygen of the unreacted ATP from O18 labeled amino acid the first partial reaction catalyzed by aminoacyl tRNA synthetase.